Coach Flats or Coach Sneakers and where?

I have to wear skirts to school because I go to an all girls private school. They have to be covering the knee completely and I am petite. Usually at Marshalls, or my mom said Macy's, there are coach sneakers discounted. Could you also find coach flats there b/c I don't think sneakers and "long" skirts, or skirts at all, go together well.